Those are just some of the common problems. There are many more recorded instances of herbal medicines causing trouble.
One of the other major problems concerning herbal medicines is that they can interact dangerously with prescribed drugs. So, for example, liquorice can interfere with drugs used to control high blood pressure.
Horse chestnut also contains an ingredient which may interfere with anticoagulants and lily of the valley can mix badly with the heart drug digitalis.
The evidence certainly does suggest, very firmly, that any patient taking a herbal medicine should be on the lookout for side effects. And they should also be very aware that herbal medicines may cause dangerous reactions when taken with prescribed medicines.
Herbal medicines can do good and they are sometimes very powerful in helping certain conditions. But they can also do harm and only experienced herbalists who recognise this are worth their salt.
Many articles taken from 'A word with the doctor', by Dr. John Windsor.